The present invention relates to ceramic dielectric materials used for microwave frequency applications and having a large relative dielectric constant, very large Q (inverse value of dielectric loss) for practical use and stable and small temperature coefficient, and a method for producing such ceramic dielectric materials.
Nowadays dielectrics for microwave frequency applications are used for resonator, filter, branching filters, and Microwave Integrated Circuit substrate (MIC substrate). It is very desirable to improve the dielectric characteristic for stabilizing sending and receiving frequencies, for improving filter characteristic and for miniaturizing communication equipments and circuits which are recently very often used.
The following are necessary characteristics for the above mentioned dielectrics.
(1) Large relative dielectric constant.
The bulk of dielectric application devices is inversely proportional to the square root of relative dielectric constant. Therefore it is very important for the miniaturization of apparatus or devices to have a large relative dielectric constant.
(2) Low dielectric loss.
(3) Good characteristics for the temperature stability at resonance frequency.
In the prior art, some of the dielectrics having the above characteristics are described in the Japanese patent publication No. 59-37526/1984 in the form of general formula: EQU (BaO).sub.x (TiO.sub.2).sub.y (Sm.sub.2 O.sub.3).sub.z ;
wherein, 5.ltoreq.x.ltoreq.23, 57.ltoreq.y.ltoreq.82.5, 2.5.ltoreq.z.ltoreq.37.5, x+y+z=100; x,y,z are expressed by mol percentage.
Some of the dielectrics are also described in the Japanese laying-open patent publication No. 63-294609/1988 in the form of general formula: EQU {BaO}.sub.x {TiO.sub.2 }.sub.y {(Sm.sub.2 O.sub.3).sub.l-m-n (SrO.cndot.CeO.sub.2).sub.m (CaO.cndot.CeO.sub.2).sub.n }.sub.z
wherein, 0.1.ltoreq.x.ltoreq.0.25, 0.6.ltoreq.y.ltoreq.0.85, 0.05.ltoreq.z.ltoreq.0.30, 0.ltoreq.m.ltoreq.0.80, 0.ltoreq.n&lt;0.8, x+y+z=1, m+n.ltoreq.0.8; x,y,z are expressed by mol fraction.
Nowadays, microwave communication apparatus is becoming smaller and lighter. From this point of view, each part of the electrical communication apparatus is required to be miniaturized.
In the prior art, some dielectrics have a relatively large relative dielectric constant of about 84 in maximum value, large Q value and low temperature coefficient. But, such prior dielectric materials were not suitable for more miniaturizing of the apparatus or devices, because larger dielectric constant was required for assembling smaller apparatus or devices.
For assembling small apparatus or devices, therefore, it is necessary to use very large relative dielectric constant of the dielectric materials. From this point of view it has thus far been very difficult to find very large dielectric constant materials for practical use.